The separation of a liquid into its fractions, or components of varying specific gravity, has been carried out, inter alia, by centrifugation in many hospital, laboratory and industrial settings. For example, centrifugation is widely used in blood separation techniques to separate blood into fractions containing plasma, platelets, red blood cells white blood cells and/or formed components, e.g. fibrinogen, fibronectin, factor VIII, factor XIII and the like. Quite simply, devices for use in such techniques rely on the more dense components, e.g. the cell-containing fraction(s) in blood, being forced to a distal portion of the apparatus by the centrifugal force.
Many of the numerous device designs which utilize centrifugation can be placed into two categories: a first group in which the sample container is swung about a central axis of the centrifuge system itself; and, a second group in which the chamber is rotated about its own longitudinal axis. In the first category the container is typically a plastic bag or tube closed on one end. Such containers are orbited about the central axis of the centrifuge system such that the more dense components are forced to the bottom of the tube or to one side of the bag. Means are thereafter provided to selectively remove the less dense component, such as plasma from the more dense component, such as blood cells and platelets, or vice versa. Typically such means is a separator assembly which is insertable into an elongated blood-containing tube. Alternatively, when using a plastic bag, the bag is carefully squeezed so as to force out the plasma. U.S. Pat. No. 3,932,277 to McDermott et al discloses a device comprising a sample tube and a collection tube. The collection tube has a filter and check valve at one end which is inserted into an already centrifuged sample tube to collect the plasma. Similarly U.S. Pat. No. 3,799,342 to Greenspan utilizes a separator having a check valve which opens upon pressurization of the sample container to allow separated plasma to pass through into a collection chamber. U.S. Pat. No. 4,818,386 to Burns employs a semi-buoyant separator designed to have a specific gravity intermediate the specific gravities of two components into which the liquid is to be separated. Upon centrifugation, the separator moves within an elongated blood sample tube to a position substantially between the more dense materials at the bottom and the less dense materials at the top. An elastomeric cup encompassing the separator locks the separator in place when centrifugation is ceased to facilitate selective removal of the less dense component.
As mentioned, a second category includes devices wherein the liquid-containing chamber is rotated about its longitudinal axis. The liquid containing chamber is typically cylindrical or bowlshaped such that upon centrifugation heavier liquid components, e.g. blood cells, migrate outwardly toward the chamber wall and the lighter components, e.g. plasma, remain inward. Within this category are devices which include conduits to other distinct containers, typically for the receipt and/or transfer of liquid during centrifugation, and devices which are self-contained for processing a fixed volume of liquid. One such device of the former variety is the "Latham bowl" disclosed and modified in a number of patents including U.S. Pat. Nos. 4,086,924, 4,300,717, etc. The Latham bowl is designed such that the less dense components towards the inner portion of the spinning bowl are forced upward into a collection area inward of the outermost bowl radius. This system, however, requires a constant flow of blood to force the separated plasma out and this "flow-during-spinning" feature mandates complex and expensive rotary seals.
McEwen in U.S. Pat. No. 4,828,716 separates a liquid, such as blood, into its components, such as plasma and red blood cells, by centrifugation in an elongated tube at speeds sufficient to provide a concentric interface between these components. That is, a substantially cylindrical apparatus is spun about its central or longitudinal axis such that the more dense cellular components move to the outer wall and the less dense components are inward of the more dense components. McEwen device thereafter reduces the volume of the processing chamber and collects the less dense plasma components by forcing it to a central collection port.
The above-described concentric separation occurs, by virtue of the centrifugal, or G-force, acting upon the components, which is dependent upon radius and which can be expressed as EQU G=1.18.times.10..sup.5 .times.Radius (CM).times.RPM.sup.2
To provide a good separation of components, it is beneficial to provide as "sharp" an interface as possible between the components of varying density. Thus, for each liquid made up of two or more components, there is minimal G-force needed to maintain this concentric interface. One potential difficulty with such prior art reducing-volume/concentric-interface devices is that it becomes difficult to maintain the desired separation interface because as the volume is reduced and the plasma is collected, the height of the processing chamber is also decreasing. This provides, obviously, that the constant volume of cellular (more dense) material is forced inward to a decreasing radius. Indeed this must occur with the prior art device to force the plasma material centrally towards the collection port. However, it can be appreciated that when the radius of cellular material drops below the critical value needed to maintain a concentric interface at a given speed, the interface becomes much less clearly defined, if not nonexistent, and collection of unwanted cellular material results. For the McEwen-type blood separation, the volume of pure plasma is not as critical as for certain ocher applications. Also, the McEwen-type device operated at ullracentrifugation ranges.
In more current technologies, it has become critical to be able to separate blood components with a more reliable purity of separation resulting in a higher hematocrit value, i.e. ratio of to red blood cells to the total volume of the sample. It is also highly desirable to be able to provide separation in shorter periods of time and with minimal need for detection devices. Further, ultracentrifugation can exert excessive shear forces on blood components which have undesirable effects, e.g. hemolysis. It would be useful in many applications to provide the above liquid separation benefits, especially at centrifuge speeds below 20,000 RPM, preferably in the 3,000-15,000 RPM and optimally in the 5,000-10,000 RPM range. Typically, centrifuge speeds above about 10,000 RPM results in severe journalling and bearing problems especially relating to the problem of providing adequate lubrication.
An object of the present invention is to provide more accurate and efficient separation of liquid, in particular blood, into its phase portions of different densities through the employment of improved separation techniques. A particular advantage of the present invention is that a quick, efficient separation of liquid components can be accomplished without the disadvantages, i.e., expensive, complex equipment and damage to components such as blood components, of an ultracentrifugation system.
A particular feature of the present invention relates to the fact that in accordance with the novel separation and collection techniques according to the present invention, a blood sample may be used to provide a Fibrin extraction to be used in the preparation of a tissue repair promoting substance, a so-called tissue-glue, which separation and preparation is carried out in a field compartment eliminating the risk that laboratory persons or operators are exposed to infectious agents that may be passed through contact with blood, e.g. hepatitis or acquired immune deficiency syndrome.
A particular advantage of the present invention relates to the novel separation and collection technique which renders it possible to perform a separation of a blood sample for separating the blood sample into plasma and blood cells which separation further provides a separation of blood platelets from the blood cells and consequently provides the ability to obtain plasma with a desired high or low platelet level by varying the appropriate process parameters.